One of inspection methods that are widely used for clinical inspection is an immunological method. In the immunological method, an antibody that specifically recognizes a component to be measured is used. For example, after the antibody (primary antibody) captures a component that is to be measured and is contained in a specimen, the component is detected using a secondary antibody that selectively captures the primary antibody. The secondary antibody is provided with a label for higher detection sensitivity. The label is, for example, a fluorescent material, a material that is necessary for enzyme chemiluminescence or the like. Since the immunological method is a measurement technique that can simply detect a component with high sensitivity, the immunological method is suitable for a quantitative measurement of minute amounts of components contained in a specimen.
However, the immunological method involves a problem of cross-reactivity. The cross-reactivity is an effect that causes the primary antibody to capture not only a component to be measured that is necessary to recognize but also a molecule (such as a metabolite of the component to be measured) with a structure similar to that of the component to be measured. This means that a quantitative result is higher than the true value and the component to be measured cannot be accurately quantified.
In particular, small molecule compounds, having low-molecular weight, tend to exhibit stronger cross-reactivity. To develop an antibody for these target molecules, it is necessary to increase the molecular size of the component by adding a carrier protein to the component to be measured; a part other than a part to which the carrier protein is added can be an epitope. Therefore, it is often difficult to identify the structural difference between a metabolite and the target component depending on the part to which the carrier protein is added. In order to suppress the cross-reactivity, it is necessary to create a primary antibody that is capable of identifying the difference between molecules with similar structures. However, it is difficult to create such a primary antibody and a lot of effort with cost and labor is required for the creation of the primary antibody, which is not efficient.
In contrast to the immunological method, a mass spectrometry method detects a component on the basis of the mass of the component to be measured. Thus, the mass spectrometry method is a measurement technique capable of identifying the difference between the component to be measured and another molecule (such as a metabolite) with a structure similar to that of the component. Especially, a method for MS/MS analysis and a method for MS(n) analysis are techniques capable of identifying the difference between components with similar structures with high accuracy by fragmenting the components to be measured into fragment ions. In addition, since the mass spectrometry method does not require a special reagent such as an antibody, it is possible to reduce the cost and effort.
There are known examples in which another analysis method or process is combined with the mass spectrometry analysis, where the analysis method or process is performed before execution of the mass spectrometry analysis. For example, western blotting (refer to Patent Document 1), collection of target bacteria using magnetic beads (refer to Patent Document 2), pull-down assay (refer to Patent Document 3), collection of target substances onto an organic thin film (Patent Document 4), or gel electrophoresis (Patent Document 5) is performed before the mass spectrometry starts.